Conventionally, the communication protocol of CAN has widely been employed in communication between multiple electronic control units (ECU) mounted in a vehicle.
A communication system which employs the CAN communication protocol is so configured that multiple ECUs are connected to a common CAN bus, and information is transmitted and received by an ECU at the reception side sampling a signal output by an ECU at the transmission side to the CAN bus. Moreover, the ECU at the transmission side outputs signals to the CAN bus while sampling signals on the CAN bus to detect the presence/absence of a change related to information transmitted by itself.
Tsutomu Matsumoto, Taiki Kodatsu, Yuu Tsuchiya, Yoshifumi Nakayama and Katsunari Yoshioka “How to Enhance Integrity of Controller Area Network Against Electrical Data Forgery” Computer Security Symposium 2014, Oct. 22-24, 2014 (Non-Patent Document 1) has pointed out that an ECU at the reception side may receive forged information without an ECU at the transmission side knowing it, by intentionally changing signals on the CAN bus only for a short period during which sampling is performed by the ECU at the reception side, in the case where the timing of sampling signals on the CAN bus is different between the ECU at the transmission side and the ECU at the reception side.